A superjunction transistor device, which often is also referred to as compensation transistor device, includes a device region with at least one region of a first doping type (conductivity type) and at least one region of a second doping type (conductivity type) complementary to the first doping type. The at least one region of the first doping type is often referred to as drift region, and the at least one region of the second doping type is often referred to as compensation region (although there are also publications where the overall region with the at least one region of the first doping type and at least one region of the second doping type is referred to as drift region). The drift region is coupled to a drain node and the compensation region is coupled to a source node of the transistor device.
A superjunction transistor device furthermore includes a control structure with a source region and a body region each coupled to the source node, and a gate electrode dielectrically insulated from the body region by a gate dielectric. This control structure defines an operation state of the transistor device. In an on-state there is conducting channel in the body region along the gate dielectric between the source region and the drift region. In the off-state, the conducting channel is interrupted. If, in the off-state, an external voltage is applied between the source node and drain node that reverse biases a pn junction between the body region and the drift region and a pn-junction between the compensation region and the drift region a space charge region (depletion region) expands in each of the drift region and the compensation region.
In the off-state, the transistor device prevents a current flow between the drain node and the source node, unless the voltage between the source node and the drain node reaches a voltage level that is usually referred to as breakdown voltage level or, shorter, breakdown voltage. When the voltage reaches the breakdown voltage an avalanche breakdown occurs that causes an avalanche current to flow. The avalanche breakdown is associated with an acceleration of charge carriers in the drift region such that they create electron-hole pairs by impact ionization. Charge carriers created by impact ionization create new charge carriers, so that there is a multiplication effect.
Superjunction devices can be designed to withstand an avalanche current for a certain time. In the avalanche state a high amount of power may be dissipated in the transistor device which may finally result in a destruction due to overheating if the avalanche current prevails longer than the time it takes to reach the thermal limit, that is, to overheat the transistor device.
There is a need to provide a superjunction transistor device with a low on-resistance and a high avalanche robustness at a given voltage blocking capability.